If Debian use an own format rather than e.g. SPDX then we might
easier be able to deal with potential disagreements on licensing
interpretations.

Debian has different opinion than, say, FSF, on what is an acceptable
FLOSS license. We might in the future disagree with other distros on
how to interpret some licensing issues like what exactly the OpenSSL
license conflicts with, or how to handle licenses mentioning patents.

I know that we are not lawyers. But we still have opinions that may
reflect our view on licenses - sometimes differently from other
distros.

Imagine the SPDX folks deciding that two licenses are so similar that
they use a single shortform for both. And imagine that we want to
distinguish those particular licenses. Then it is better to have a
format of our own - which ideally is then machine-translatable to the
"universal" format, where the translator then deals with the quirks
of merging or hinting as fuzzy.

My understanding is that the SPDX folks are also not lawyers, and are
open to drawing the lines between different license keywords where it's
useful to consumers of SPDX - including Debian.

We may wish to allow for temporal divergence from SPDX, just as we do
for the FHS in Debian Policy; but I wouldn't like us to start from the
assumption that SPDX shortnames will be unsuitable, particularly when
the implementors have gone to quite a bit of effort already to
incorporate the DEP-5 work as a basis for theirs.